So, ATM, I'm trying to uninstall stub IOSes to get MyMenuify to work. However, I'm confused. After I uninstall an IOS, do I install it again via DOP-Mii and it'll work? Also, if you can tell me specifically which IOSes I'd need, thank you.

Nonononono don't uninstall Stub IOS - it will cause problems (even if they "do nothing"). You just need a cIOS (249 I think) and have to patch the .app for your system menu with a .mym and install the newly created .csm with MyMenuify (ModMii can do this).